Large quantities of liquid egg products are pasteurized each year to produce products sold in refrigerated form with limited shelf life. See generally. Egg Pasteurization Manual (USDA Agricultural Research Service 1969). More recently, the provision of techniques for ultrapasteurizing liquid egg products has led to considerable interest in marketing liquid egg products which have extended shelf lives under refrigerated conditions.
M. Hamid-Samimi et al., in IUFOST Symposium on Aseptic Processing & Packaging of Foods Proceedings, 229 (Symposium held Sept. 9-12, 1985, in Tylosand, Sweden), concerns ultrapasteurizing liquid egg in which the egg is heated by contacting to a heated surface. See also U.S. Pat. No. 4,808,425, issued Feb. 28, 1989.
Eynon Jones U.S. Pat. No. 3,113,872 discloses a method of treating liquid egg products (shown schematically in FIG. 2 therein) which employs (a) a first heating step in which liquid egg is contacted to a heated surface, (b) a first vacuum evaporation and cooling step, (c) a second heating step in which liquid egg is contacted to steam, and (d) a second vacuum evaporation and cooling step.
T. Sugihara et al., Food Technology 20, 1 (1966) discloses a method of treating liquid whole egg (shown schematically in FIG. 1 on page 4 thereof) which employs (a) a first heating step in which liquid egg is contacted to a heated surface, (b) a second heating step in which the liquid egg is contacted to steam, and (c) a vacuum evaporation and cooling step. L. Kline et al., Food Technology, 105 (November 1965), at page 114, report a method of processing liquid egg white similar to the method of processing liquid whole egg disclosed by Sugihara et al., supra.
U.S. Pat. No. 4,957,760 of Swartzel, Ball, and Liebrecht, titled "Ultrapasteurization of Liquid Whole Egg Products with Direct Heat," and filed Feb. 16, 1989, discloses a method of ultrapasteurizing a liquid whole egg product in which the product is initially heated to a first predetermined temperature in a first heating step. The product is then maintained at the first predetermined temperature for a first predetermined holding time. Next, the product is heated to a second predetermined temperature in a direct heating step. The product is then maintained at the second predetermined temperature for a second predetermined holding time sufficient to cause the desired bacterial kill in the product. The product is then cooled and aseptically packaged to provide a packaged liquid whole egg product having a shelf life of at least four weeks under refrigerated conditions. In a preferred embodiment of the invention disclosed therein, the product is heated by steam injection in the direct heating step and then cooled without the use of a vacuum chamber.
Ultrapasteurization processes which contact the liquid whole egg product to a heated surface produce products of excellent quality, but have limited run times due to eventual fouling of the heated surface. Ultrapasteurization processes which contact the liquid whole egg product to steam make longer run times available, but the relative severity of the steam contact step usually results in a lower quality product. In view of the significant demand for ultrapasteurized liquid whole egg products, there is a need for new ultrapasteurization processes which provide greater control over the process so as to make longer run times with higher quality products possible. The present invention is based on our ongoing efforts to provide improved techniques for pasteurizing and ultrapasteurizing such products.